An estimated 80 million people are infected with Wuchereria bancrofti and Brugia malayi, mosquito-transmitted nematode parasites that cause deforming lymphatic filariasis in the tropics. There is clear evidence from animal studies that stage-specific immunity can develop to filarial microfilariae and to third stage infective larvae (L3). This ICIDR project represents an ambitious attempt to study immunity to filariasis in humans with a longitudinal study of carefully defined populations in a highly endemic region. The SPECIFIC AIMS of this project are: 1. TO TEST THE HYPOTHESIS THAT HUMANS Develop PROTECTIVE IMMUNITY TO BANCROFTIAN FILARIASIS. 2. TO STUDY IMMUNITY TO MICROFILARIAE IN HUMANS. 3. TO IDENTIFY PARASITE ANTIGENS THAT MAY BE TARGETS OF PROTECTIVE IMMUNE RESPONSES TO L3 AND MICROFILARIAE OF WUCHERERIA BANCROFTI. 4. TO TEST THE HYPOTHESIS THAT MATERNAL INFECTION STATUS AFFECTS THE SUSCEPTIBILITY OF CHILDREN TO FILARIASIS.